Amido-carboxylic acids are industrial chemical intermediates for the preparation of many chemicals used in commerce. Amido-carboxylic acids are prepared by reacting a lactam with a carboxylic acid. Amido-carboxylic acids are also prepared by reacting a carboxylic acid, carboxylic acid chloride, carboxylic acid anhydride or carboxylic acid ester with an amino carboxylic acid which is prepared by hydrolysis of a lactam. These processes to form amido-carboxylic acids are referred to as amidation reactions.
It is known to convert lactams by hydrolysis into the corresponding amino-carboxylic acids in the presence of hydrolysis promoting reagents such as hydrochloric acid. However, pure amino-acids are not directly obtained. In the case where hydrochloric acid is used as the promoting reagent, the amino-acid-hydrochloride is obtained and the separation of the free carboxylic acid is cumbersome and expensive.
U.S. Pat. No. 2,453,234 discloses a process for preparing an amino-carboxylic acid by hydrolyzing a lactam by means of at least 10 moles of water per mole of lactam to produce an amino-carboxylic acid. Great Britain Pat. No. 648,889 discloses a process for preparing amino-carboxylic acids by heating aliphatic or cyclo-aliphatic lactams in the presence of more than 20 moles of water per mole of lactam. U.S. Pat. No. 2,956,068 discloses a process for preparing amido-carboxylic acids by reacting a lactam with a free carboxylic acid in the presence of catalytic amounts of water. The reaction product is obtained as a solid crystal mass which is subsequently suspended in water and neutralized.
In contrast, the present inventors have unexpectedly discovered a process for preparing amido-carboxylic acids from a lactam and a carboxylic acid anhydride in water. It is unexpected that an amido-carboxylic acid could form by the reaction of a carboxylic acid anhydride with an amino acid in the presence of water. Moreover, it is unexpected that in the reaction of amino acids with carboxylic acid anhydrides, the lactam precursor of the amino acids does not react with the carboxylic anhydride. The amido-carboxylic acids obtained by this process essentially contain one molecule of amino acid and one molecule of carboxylic acid, and are essentially free of undesirable byproducts.